Marine Dead Zones: Understanding the Problem II

CONTENTS FOR THIS SECTION

Gulf of Mexico Dead Zone
Impacts of the Gulf of Mexico Dead Zone on Fishing
Policy and Management Efforts
References

Gulf of Mexico Dead Zone

The hypoxic zone in the northern Gulf of Mexico is the largest observed in the estuarine and coastal regions of the western hemisphere. 11 First recognized in the early 1970s, it is the largest and most hypoxic area in the United States. In the summer of 1993 following massive Mississippi River flooding (and in subsequent years), the dead zone doubled in size to more than 18,000 square kilometers (larger than the size of New Jersey, although pockets of oxygenated water may occur within this boundary), extending westward from the mouth of the Mississippi River to the upper Texas coast. 12 The seasonal shape and extent of the dead zone are mostly a function of the Mississippi/Atchafalaya River plume, the combined outflow from these two major rivers, and the biological processes it influences. This hypoxic zone originates each spring as melting snow and peak runoff events flush nutrients into the Mississippi River system and eventually into the Gulf. The hypoxic zone generally occurs from May to September, but varies from year to year. Low velocity winds during the summer result in calm seas that maintain the stratified barrier between surface and bottom water layers. Only during weather disturbances, such as frontal passages, tropical storms, and hurricanes, does vertical mixing of these stratified layers occur. Increased winds and frontal storms in autumn vertically mix the water column, dissipating the hypoxia. In the summer of 1998, this dead zone extended from very near shore (about 10-15 feet water depth) to deeper waters than are normally hypoxic (as much as 160 feet deep off the Mississippi River delta). 13

Nutrient enrichment is the primary cause of eutrophication, of some algal blooms, and hypoxia, and is believed to be a major factor in areas such as the northern Gulf of Mexico. 14 The Mississippi watershed drains 41% of the land area of the contiguous 48 states, including most of the farmbelt. Studies of the Mississippi and Atchafalaya Rivers indicate that dissolved nitrogen levels have tripled and phosphorus levels have doubled since 1960, fueling algal growth and the resultant dead zone. 15

Research suggests that fertilizer leaching and runoff from upriver agricultural sources may be the main sources of nutrients. For example, USGS states that 56% of the Mississippi River's nutrient loading results from fertilizer runoff, with an additional 25% of the Mississippi River nitrogen coming from animal manure (municipal and solid wastes account for 6%, atmospheric deposition for 4%, and unknown sources for 9%). 16 Analysis of cores of sediments underlying the hypoxic area reveals historic information on the Mississippi River watershed, indicating that surface water productivity has increased and bottom water oxygen stress has worsened since the early 1900s, with the most dramatic changes occurring since the 1950s - a change strongly correlated with increased use of commercial fertilizers in the watershed. 17 Although hypoxia occurred in the northern Gulf of Mexico prior to heavy use of artificial fertilizers, human activities have enhanced and prolonged the hypoxic condition. Other studies also show a direct relationship between the river-born nutrients, the high rates of phytoplankton production, and subsequent Gulf of Mexico hypoxia. 18 However, questions remain as to how much of the river's nitrogen might come from natural soil mineralization, what effects floods have on nutrient transport, and how much nitrogen may be contributed by coastal land loss, estimated at 25 square miles per year. 19

Although studies have found that more than 70% of the total nitrogen transported to the Gulf of Mexico by the Mississippi River originates above the confluence of the Ohio and Mississippi Rivers, 20 focusing on nitrogen runoff per unit area identifies other areas where more concentrated nutrient runoff occurs. 21 Although the lower Mississippi Basin (which drains parts of Tennessee, Arkansas, Missouri, Mississippi, and Louisiana) is responsible for only 23% of the nitrogen delivered to the Gulf: some scientists believe that nitrogen removal and/or runoff prevention strategies should focus on this area because of its much greater relative nitrogen contribution 22 and likely more economically efficient nitrogen removal. Researchers estimate that the benefits of nutrient controls in this lower basin could be twice as effective as implementing them in upstream basins. 23 Strategies for implementing nutrient controls in the lower Mississippi Basin have been identified. 24

Many farming interests maintain that evidence has not proven that agricultural practices are the primary contributors to the development of the Gulf of Mexico dead zone. 25 Farmers dispute that they contribute substantially to creating a dead zone that is as much as 1,000 miles away. They fear that, if they are considered to be the cause of the problem, they may have to alter their practices. They argue that their goal is to keep as much as possible of the applied nutrients on their land, since any nutrients that wash away represent wasted money. On the other hand, it has been estimated that approximately $750 million in excess nitrogen (calculated as fertilizer cost) enters the Mississippi River each year. 26

Impacts of the Gulf of Mexico Dead Zone on Fishing

The Gulf of Mexico supports important, easily accessible commercial and recreational fisheries, bringing in almost $2.9 billion annually in retail sales to Louisiana and supporting almost 50,000 jobs. 27 These highly productive fisheries are the direct result of the input of nutrients from the Mississippi River watershed. To date, no studies have investigated the linkage between fishery declines and hypoxic episodes in the Gulf, but some evidence suggests the dead zone may force fish and shrimp further offshore as well as into shallow nearshore areas (producing what is locally called a "jubilee") that may provide less desirable habitat. 28 Hypoxia increases stress on aquatic ecosystems and may decrease biological diversity in areas experiencing repeated and severe hypoxia. 29 Crowding of marine life into restricted habitat also may lead to indirect consequences through altered competition and predation interactions. In addition, hypoxia may delay or impede the offshore migration of older, larger shrimp, preventing shrimp trawlers from selectively targeting larger shrimp for harvest.

While it is unclear what specific effects the dead zone has on Gulf fisheries, the occurrence of this dead zone may force fishing vessels to change their normal fishing patterns, possibly expending more time and fuel to harvest their catch. One study has concluded that any increase in fishing expenses could drive marginal operators out of business. Other potential impacts on Louisiana fisheries cited include: concentration of fishing effort in other areas, resulting in localized overfishing; damage to essential habitat, and possible decreased future production; shellfish mortality, if hypoxic conditions impinge on barrier island beaches and coastal bay waters; localized mortality of finfish and shellfish in shoreline areas; and decreased growth due to reduced food resources in the sediments and water column. 30 In August 1997, the Louisiana Department of Wildlife and Fisheries initiated a 3-year study, funded by the National Marine Fisheries Service (13.5. Department of Commerce), to determine the dead zone's impact on commercial fisheries.

Policy and Management Efforts

Since a temporary, yet severe, hypoxic event could result in significant mortality or injury to marine mammals, fish, and other aquatic species, better understanding and consistent monitoring of hypoxic phenomena are deemed necessary. NOAA initiated the Nutrient Enhanced Coastal Ocean Productivity (NECOP) program in 1989 to study the effects of nutrient discharges on U.S. coastal waters. This study found a clear link between nutrient input, enhanced primary production (i.e., algal and plant growth), and hypoxic events in the northern Gulf of Mexico. 31

In response to a January 1995 petition from the Sierra Club Legal Defense Fund (currently known as Earthjustice Legal Defense Fund) on behalf of 18 environmental, social justice, and fishermen's organizations, the Gulf of Mexico Program 32 held a conference in December 1995 to outline the issue and identify potential actions. Following that conference, Robert Perciasepe, Assistant EPA Administrator for Water, convened an interagency group of senior Administration officials (the "principals group") to discuss potential policy actions and related science needs. Subsequently, this "principals group" created a Mississippi River/Gulf of Mexico Watershed Nutrient Task Force. Additionally, the White House Office of Science and Technology Policy's Committee on Environment and Natural Resources (CENR) is conducting a Hypoxia Science Assessment at the request of EPA. The CENR Assessment will be peer reviewed, made available for public comment, and submitted to the Task Force to assist the Task Force in developing policy recommendations and a strategy for addressing hypoxia in the northern Gulf of Mexico.

A key consideration is the level and duration of the necessary reduction in excess nutrients from watersheds. Many agricultural lands have been saturated with nutrients for many years, and it may take a long time to "cycle out" excess nitrogen and phosphorus, even if application rates are reduced. 33 While some believe this problem may have no fast solutions and any management regime considered will need to recognize that progress or improvement may not be apparent for years or even decades, others suggest that improved agricultural practices in efficient application of chemical fertilizers and prevention of soil erosion could yield immediate and measurable benefits.

Because nonpoint sources are major contributors to the problem at the mouth of the Mississippi River System, many believe the Clean Water Act is the appropriate legal framework for addressing future nutrient inputs. Under §319 of the Clean Water Act, Louisiana and other states have initiated nonpoint-source control programs. These programs seek to combine local, state, and federal agency resources to address pollution from nonpoint sources within each state. 34 To effectively address concerns, however, nonpoint-source programs would need to be encouraged, funded, and implemented throughout the Mississippi River watershed. Under §303 of the Clean Water Act' states must identify water-quality-limited segments of their waters which are not meeting standards, and then establish total maximum daily loads (TMDLs) for each listed water and each pollutant (e.g., nutrients) which is not meeting current water quality standards. In addition, agricultural research and educational outreach/assistance to farmers might complement regulatory efforts.

Congress took note of the hypoxia problem in 1997 when the conference report on FY 1998 Department of the Interior appropriations (H.Rept. 105-337) directed the USGS to give priority attention to hypoxia in its FY1999 budget. Congress considered appropriating funds for FY1999 to better understand and address the hypoxic area in the northern Gulf of Mexico. H.R 4193 (FY 1999 Department of the Interior appropriations) was reported to the House (H.Rept. 105-609) with a total of $0.5 million for Gulf hypoxia research by USGS, while H.R. 4276 (FY1999 Department of Commerce appropriations) was reported to the House (H.Rept. 105-636) with $8.725 million to address harmful algal blooms and hypoxia by NOAA. The Senate report on FY 1999 Department of Commerce appropriations (S.Rept. 105-235, S. 2260) also specifically mentioned NOAA funding for hypoxia research. In addition, several bills (H.R. 2565, S. 1219, and S. 2218) proposed research on harmful algal blooms, some of which would also address hypoxia concerns. HR. 4235/S. 1480, the Harmful Algal Bloom and Hypoxia Research and Control Act of 1998, proposed a specific focus on hypoxia.

Near the end of the 105th Congress, provisions of the Harmful Algal Bloom and Hypoxia Research and Control Act of 1998 were incorporated into the Coast Guard Authorization Act of 1998 (H.R. 2204). This measure was signed into law as P.L. 105-383 on November 13, 1998, wherein Title VI authorizes appropriations through NOAA to conduct research, monitoring, education, and management activities for the prevention, reduction, and control of hypoxia, harmful algal blooms, Pfiesteria, and other aquatic toxins.

Continuing executive and congressional attention is likely to be focused on understanding the causes of hypoxia. To the extent the impacts on commercial interests or the environment are found to be severe, remedies will likely be explored.

References

11 N. Rabalais, et al. "Consequences of the 1993 Mississippi River Flood:l in the Gulf of Mexico." Regulated Rivers: Research & Management, v.14 (1998): 161-177.

12 White House Office of Science and Technology Policy, Committee on Environment and Natural Resources, Hypoxia Work Group. Gulf of Mexico Hypoxia Assessment Plan. March 1998, p.3. (Hereafter referred to as "Hypoxia Work Group.")

13 N. Rabalais. Press Release. Louisiana Universities Marine Consortium, July 27, 1998.

14 Hypoxia Work Group, p.2.

15 R. E. Turner and N. Rabalais. "Changes in Mississippi River Quality This Century - Implications for Coastal Food Webs." Bioscience, v.41, no.3 (1991):140-147; D. Justic, et al. "Changes in Nutrient Structure of River-Dominated Coastal Waters: Stoichiometric Nutrient Balance and Its Consequences." Estuarine, Coastal, and Shelf Science, v.40(1995): 339-356.

16 R.H. Meade, ed. Contaminants in the Mississippi River, 1987-92. Circular 1133. Denver, CO: U.S. Geological Survey, 1995. 140 p.

17 T. A. Nelson, et al. "Time-Based Correlation of Biogenic, Litbogenic and Authigenic Sediment Components with Anthropogenic Inputs in the Gulf of Mexico NECOP Study Area." Estuaries, v.17 (Dec. 1994):873; B.J. Eadie, et al. "Records of Nutrient-Enhanced Coastal Productivity in Sediments from the Louisiana Continental Shelf." Estuaries, v.17 (Dec.1994): 754-765; N. Rabalais, et al. "Nutrient Changes in the Mississippi River and System Responses on the Adjacent Continental Shelf." Estuaries, v.19 (1996): 386-407; 5. Gupta, et al. "Seasonal Oxygen Depletion in Continental-Shelf Waters of Louisiana: Historical Record of Benthic Foraminifers." Geology, v.24 (1996): 227-230; and R.E. Turner and N. Rabalais. "Coastal Eutrophication Near the Mississippi River Delta." Nature, v.368 (1994): 619-621.

18 F. H Sklar and R. E. Turner."Characteristics of Phytoplankton Production Off Barataria Bay in an Area Influenced by the Mississippi River." Marine Science, v.24 (198 1):93-106; S. E. Lohienz, M. J. Dagg, and T. E. Whitledge. "Enhanced Primary Production at the Plume/Oceanic Interface of the Mississippi River." Continental Shelf Research, v.7 (1990):639-664; S.E. Lohrenz, et al. "Variations in Primary Productivity of Northern Gulf of Mexico Continental Shelf Waters Linked to Nutrient Inputs from the Mississippi River." Marine Ecology Progress Series, v.155 (1997): 435-454.

19 D. Malakoff. "Death by Suffocation in the Gulf of Mexico." Science, v.281 (July 10, 1998):190-192. (Hereafter referred to as "Death by Suffocation.")

20 R. Alexander, R. Smith, and G. Schwarz. "The Regional Transport of Point and Nonpoint-Source Nitrogen to the Gulf of Mexico." Proceedings of the First Gulf of Mexico Hypoxia Management Conference, Kenner, LA, Dec. 5-6, 1995, p. 127-133 (Hereafter referred to as "Regional Transport."); R.H. Meade, ed. Contaminants in the Mississippi River, 1987-92. Circular 1133. Denver, CO: U.S. Geological Survey, 1995. 140 p.

21 0f this total, 39% is contributed by the Upper and Central Mississippi Basins (which includes Minnesota, Wisconsin, Iowa, Missouri, and Illinois), 22% from the Ohio River Basin, and 11% from the Missouri River Basin.

22 Nitrogen runoff for the lower Mississippi Basin is 2,072 kilograms of nitrogen per square kilometer per year compared to 708 kilograms of nitrogen per square kilometer per year for the upper Mississippi Basin and 437 kilograms of nitrogen per square kilometer per year for the Ohio River Basin.

23 "Regional Transport," p.131.

24 C.L. Cordes and B.A. Vairin, eds. Workshop on Solutions and Approaches for Alleviating Hypoxia in the Gulf of Mexico. NWRC Special Report 98-02. Lafayette, LA: U.S. Geological Survey, 1998. 53 p.

25 C. David Kelly. 'Hypoxia Issue Paints a Murky Picture." Voice ofAgriculture, American Farm Bureau, Sept.29, 1997, http://www.fb.com/views/focus/fo97/foO929.html.

26 "Death by Suffocation," p. 190-192.

27 Southwick Associates. The Economic Benefits of Fisheries, Wildlife and Boating Resources in the State of Louisiana. Arlington, VA; March 1997. 21 p.

28 Roger Zimmerman, et al. "Trends in Shrimp Catch in the Hypoxic Area of the Northern Gulf of Mexico." Proceedings for the First Gulf of Mexico Hypoxia Management Conference, Kenner, LA, Dec. 5-6, 1995. p. 64-75.

29 "Marine Benthic Hypoxia," p. 285-287.

30 J. Hanifen, et al. "Potential Impacts of Hypoxia on Fisheries: Louisiana's Fishery-Independent Data." Proceedings for the First Gulf of Mexico Hypoxia Management Conference, Kenner, LA, Dec. 5-6, 1995. p.87-100.

31 N0AA, Coastal Ocean Program Office. Nutrient-Enhanced Coastal Ocean Productivity, Proceedings of 1994 Synthesis Workshop. 1995, p.119; see also Estuaries, v.17, no.4 (Dec. 1994):729-911.

32 The Gulf of Mexico Program is a cooperative federal-state effort beginning after Congress, through P.L. 102-178, designated 1992 as the Year of the Gulf of Mexico. For additional information on this program, see http://www.epa.gov/gumpo/partnership.html.  

33 "Death by Suffocation" (citing Don Goolsby, USGS, Denver, CO), p.190-192.

34 D. Sabin and J. Boydstun. "Louisiana Activities and Programs in Nutrient Control and Management." Proceedings of the First Gulf of Mexico Hypoxia Management Conference, Kenner, LA, Dec. 5-6, 1995. p.196-198.